Novel Technology Allowing Cone Beam Computed Tomography in 6 Seconds: A Patient Study of Comparative Image Quality.

PURPOSE: The goal of this study was to evaluate the image quality provided by a novel cone beam computed tomography (CBCT) platform (HyperSight, Varian Medical Systems), a platform with enhanced reconstruction algorithms as well as rapid acquisition times. Image quality was compared with both status quo CBCT for image guidance, and to fan beam CT (FBCT) acquired on a CT simulator (CTsim). METHODS AND MATERIALS: In a clinical study, 30 individuals were recruited for whom either deep inspiration (DIBH) or deep exhalation breath hold (DEBH) was used during imaging and radiation treatment of tumors involving liver, lung, breast, abdomen, chest wall, and pancreatic sites. All subjects were imaged during breath hold with CBCT on a standard image guidance platform (TrueBeam 2.7, Varian Medical Systems) and FBCT CT (CTsim, GE Optima). HyperSight imaging with both breath hold (HSBH) and free breathing (HSFB) was performed in a single session. The 4 image sets thus acquired were registered and compared using metrics quantifying artifact index, image nonuniformity, contrast, contrast-to-noise ratio, and difference of Hounsfield unit (HU) from CTsim. RESULTS: HSBH provided less severe artifacts compared with both HSFB and TrueBeam. The severity of artifacts in HSBH images was similar to that in CTsim images, with statistically similar artifact index values. CTsim provided the best image uniformity; however, HSBH provided improved uniformity compared with both HSFB and TrueBeam. CTsim demonstrated elevated contrast compared with HyperSight imaging, but both HSBH and HSFB imaging showed superior contrast-to-noise ratio characteristics compared with TrueBeam. The median HU difference of HSBH from CTsim was within 1 HU for muscle/fat tissue, 12 HU for bone, and 14 HU for lung. CONCLUSIONS: The HyperSight system provides 6-second CBCT acquisition with image artifacts that are significantly reduced compared with TrueBeam and comparable to those in CTsim FBCT imaging. HyperSight breath hold imaging was of higher quality compared with free breathing imaging on the same system. The median HU value in HyperSight breath hold imaging is within 15 HU of that in CTsim imaging for muscle, fat, bone, and lung tissue types, indicating the utility of image data for direct dose calculation in adaptive workflows.

Influence of intra- and interfraction motion on planning target volume margin in liver stereotactic body radiation therapy using breath hold.

PURPOSE: This study aimed to investigate intra- and interfraction motion during liver stereotactic body radiation therapy for the purpose of planning target volume (PTV) margin estimation, comparing deep inspiration breath hold (DIBH) and deep expiration breath hold (DEBH). METHODS AND MATERIALS: Pre- and posttreatment kV cone beam computed tomography (CT) images were acquired for patients with liver cancer who were treated using stereotactic body radiation therapy with DIBH or DEBH. A total of 188 images were analyzed from 18 patients. Positioning errors were determined based on a comparison with planning CT images and matching to the liver. Treatment did not proceed until errors were ≤3 mm. Standard deviations of random and systematic errors resulting from this image matching process were used to calculate PTV margin estimates. RESULTS: DIBH errors are generally larger than DEBH errors, especially in the anterior-posterior and superior-inferior directions. Posttreatment errors tend to be larger than pretreatment errors, especially for DIBH. Standard deviations of random errors are larger than those of systematic errors. Considering both pre- and posttreatment cone beam CT images, PTV margins for DIBH and DEBH are estimated as anterior-posterior, superior-inferior, right-left = (5.7, 6.3, 3.0) mm and (3.1, 3.4, 2.8) mm, respectively. CONCLUSIONS: This study suggests that DEBH results in more reproducible target positioning, which could in turn justify the use of smaller PTV margins.

Sequence Inversion to Facilitate Concurrent Radiotherapy and Systemic Therapy. A Proof of Principle Study in the Setting of a Phase II Randomized Trial in Prostate Cancer.

Background: Concomitant chemo-radiation for pelvic cancers remains challenging to be delivered at full doses. We hypothesized that fewer delays in chemotherapy would occur if the sequence of radiotherapy would be reversed, starting with the boost volume followed by the elective nodal volume. We report the result of a Phase II randomized study for high risk prostate cancer. Patients and Method: The study was a double-blinded phase II randomized trial. Patients were eligible if they had non-metastatic high-risk prostate cancer. All patients received 2.5 years of hormonal therapy and 46.5 Gy in 25 fractions to the pelvic lymph nodes. Patients received a radiation boost to the prostate, either before or after whole pelvic irradiation. Concurrent (20 mg/m2) Docetaxel was given on the first day of radiotherapy and weekly thereafter for a total of eight treatments until predefined toxicity stopping rules. Results: Ninety patients were included and randomized. Four were ineligible for the analysis. In total, 42 patients were randomized to the standard sequence, 44 patients to the experimental sequence. There were statistically fewer GI or GU toxicities leading to a docetaxel dose reduction or omission in the experimental sequence compared to the standard sequence, 5 vs. 15 events (p = 0.027). There was no difference in overall survival, cause-specific survival, or biochemical-relapse free survival between the two sequences. Conclusions: This is the first study to test sequence inversion for pelvic radio-chemotherapy in a randomized double-blind trial. Less chemotherapy interruptions or dose reductions occurred by inverting the radiation sequence of the large field and the boost. The trial was registered with Clinicaltrials.gov: NCT00452556.

Technical Note: Evaluation of kV CBCT enhancement using a liver-specific contrast agent for stereotactic body radiation therapy image guidance.

PURPOSE: To evaluate possible use for cone-beam computed tomography (CBCT) guidance, this phantom study evaluated the contrast enhancement provided by Gadoxetate Disodium (Primovist® CAN/EU, or Eovist® USA, Bayer Healthcare, Leverkusen, Germany), a contrast agent that is taken up selectively by liver cells and is retained for up to an hour. Image quality from CBCT was benchmarked against helical fan-beam computed tomography for two phantom geometries. METHODS AND MATERIALS: Concentrations were diluted to 0.0125-0.1 mmol per kilogram of body weight (mmol/kg) corresponding to expected physiological concentrations in the liver. Kilovoltage CBCT imaging parameters of x-ray tube potential, current, and filtration were investigated using clinically available options on a TrueBeam STx linear accelerator CBCT platform. Two phantoms were created, a cylindrical idealized imaging geometry and an ellipsoidal more realistic abdominal geometry. All parameters were optimized according to the contrast-to-noise ratio (CNR) image quality metric, as a function of concentration, following the Rose criterion for CNR. RESULTS: Acceptable CNR was defined as greater than or equal to three, in accordance with the Rose criterion for CNR. These were found in a range of expected liver concentrations of 0.025-0.1 mmol/kg for a tube potential of 100 kVp, half-fan bowtie filtration and tube currents giving exposures between 2025 and 5085 mAs. Linear correlations were found for all CNR as a function of concentration, in agreement with the literature. CONCLUSION: Based on this phantom study, with appropriate selection of imaging protocol, Gadoxetate Disodium may provide useful liver CBCT enhancement at physiologically achievable liver concentrations.

Investigating the Impact of Positron Emission Tomography-Computed Tomography Versus Computed Tomography Alone for High-risk Volume Selection in Head and Neck and Lung Patients Undergoing Radiotherapy: Interim Findings.

INTRODUCTION: The aim of this study was to quantify the impact of positron emission tomography-computed tomography (PET-CT) on clinical target volume (CTV) selection in non-small cell lung cancer (NSCLC) and head and neck squamous cell cancer (HNSCC) cancer patients. METHODS: Eight radiation oncologists with expertise in either NSCLC or HNSCC prospectively contoured target volumes with and without PET-CT findings. All volumes were contoured manually, and computed tomography (CT)-alone contours were identified as gross tumour volume CT and clinical target volume (CTV) CT, whereas those contoured with the aid of PET-CT were GTV PET and CTV PET. PET-CT contours were used for actual treatment delivery. Test treatment plans were generated based on the CT-alone volumes and applied to the final PET-CT contours. PET-CT had an impact if the test plans failed department quality assurance guidelines. For each patient, the dose to critical structures and any changes in the treatment plan were recorded. RESULTS: Eighty patients (49 HNSCC and 31 NSCLC) were analyzed. PET-CT impacted 42.9% of HNSCC cases and 45.2% of NSCLC cases. On average, PET-CT volumes were significantly larger than CT-alone volumes for HNSCC cases (P < .01) but not for NSCLC cases (P = .29). For organs at risk, no statistically significant differences were noted, with the exception of mean parotid dose for the right and left parotids (P = .0137and P = .0330, respectively). CONCLUSIONS: Interim analysis of data found that the use of PET-CT in the radiation therapy planning process impacted CTV selection, resulting in a major change in radiation therapy plans in 43.7% (HNSCC 42.9% and NSCLC 45.2%) of patients.